High quality optics and full resolution video photography are becoming standard features of lightweight cellular handsets. Video camcorders get lighter and smaller. Most of the present day still picture cameras, including pocket cameras, also have the ability to shoot video.
The insertion of video photography into lightweight devices, along with the minimization of the existing camcorders and cameras, present new challenges to the camera manufacturers. On top of the shaky video produced by long zoom lenses, to which the existing state of the art OIS (optical image stabilizer) gives some improvement, a new kind of far shakier video is now generated by the way people take their videos using these lightweight devices. This jerkiness is of wider point-of-view angles than the OIS can cope with. The existing Electronic Image Stabilizers, which were integrated with cameras like the Sanyo Exacti, are also incapable of dealing with such jerkiness.
This kind of jerky video was less evident when people were using VHS camcorders that were a lot heavier and thus steadier. Conventional camcorders didn't usually produce such jerky video, also due to the fact that camcorders were usually bought by amateur photographers, who have some knowledge and understanding of photography. However, with the insertion of video capabilities to cellular handsets, practically everybody is shooting video, and the need to improve the quality of the video and correct the shooting errors and instability of the camera is one of the first priorities and demands of the lightweight handset and camera manufacturers and the consumers.
There are three types of built-in image stabilizers which are currently available: Electronic Image Stabilization (EIS), optical image stabilization (OIS) and mechanical image stabilization.
Electronic Image Stabilization
Electronic Image Stabilization (EIS) systems use electronic processing to control image stability. The EIS system kicks into action once the image hits the light-sensing chip, the Charge Coupled Device (CCD), in the camcorder. If, through its sensors, the system detects what it thinks is camera shake, it responds by slightly moving the image so that it remains in the same place on the CCD. For example, if the camera shakes to the right, the image moves to the left to compensate, thus eliminating the shake.
There are two ways EIS works to reduce the perceived movement of the image. One method increases the size of the image by digitally “Zooming” in on the image so that it is larger than the CCD. By making the image larger, the system can “pan and scan” within the image to counter the movement created by the shake. Because this system must digitally zoom in on the image to slightly increase its size, it decreases the picture resolution somewhat.
The other method of electronic stabilization uses an oversized CCD. The video image covers only about 90 percent of the chip's area, giving the system space in which to move the image. When the image is stable, the chip centers the image on the CCD. If the camera shakes to the right, the image has the space to roam to the left to compensate for the shake, keeping the subject of the image in exactly the same place on the CCD, thus eliminating the shake.
Detecting the shakes and the shakes only is the key to the effectiveness of the system. EIS systems use one of two ways to detect shaky video. Either they detect movement within the image as recorded on the CCD or they detect the actual movement of the camera.
The first method of detection analyzes the changes between the fields in each image or between successive frames. If parts of the image change in one field or frame but not the other, it indicates that the subject of the shot is moving but not the background. If, however, the entire image changes from one field to the next, it most likely means there is camera shake and the camera must correct the image. To correct the camera shake, the camera's electronics detect the direction of the movement and shift the active field or frame so that it meshes with the memorized field. A major disadvantage of this system is that, if there is a large object moving in the frame, it may be interpreted as camera shake and the camera will attempt to stabilize the subject, enhancing the jerkiness instead of canceling it. It could also switch the stabilization from moving objects to the background, blurring the image and reducing the video quality.
The camera can also use motion sensors to detect camera shake. Because this method senses movement in the camera not the image, the movement of a subject in the image cannot fool it. However, it will sometimes react at the beginning of an intentional camera movement (such as a pan) and will take a short moment to realize that the camera is being moved on purpose. Instead of a smooth pan, the image will freeze and then leap into the pan suddenly.
Optical Image Stabilization
The Optical Image Stabilization (OIS) system, unlike the EIS system, manipulates the image before it gets to the CCD. Because of this, the image is stable when it hits the chip and completely fills the chip's surface area.
The system uses a liquid-filled bellows system between a pair of glass plates. The bellows creates the equivalent of a glass prism. The prism moves the image slightly to maintain its center as it passes through the lens. As the image passes through the prism, the lens reduces or eliminates the image shake by detecting and matching the frequency and size or amplitude of the shake and rotating the plates of glass, thus changing the angle of the prism. One of the plates of glass rotates vertically, moving the image up and down. The other plate of glass rotates horizontally, moving the image to the right or left. As with the EIS system, the idea is to move the image in the opposite direction from the shake. If there is no motion detected, the prism mechanism centers itself. The sensors can also detect when the mechanism is nearing its movement limit and will reduce the amount of correction to ease the shake back into the picture, thus avoiding a sudden jolt in the image when the prism hits its movement limit.
Mechanical Image Stabilization
Mechanical image stabilization involves stabilizing the entire camera, not just the image. The easiest way to create a mechanical image stabilization system is to put the camera on a tripod. However, when it is desired to physically move the camera from one point to the next, a mechanical image stabilization system, such as a Steadicam or GlideCam, is needed.
The Steadicam and GlideCam systems use the camera's center of gravity, a counterbalance system and the camera operator's body to maintain smooth motion. These systems mount the camera on an arm which is attached to a body harness or held in the operator's hand, using the operator's arm strength for balance. The camera maintains a level axis unless adjusted by the operator, creating a smooth, floating image.
Accordingly, there is a long felt need for an image stabilization mechanism suitable for video cameras in handheld portable devices, and it would be very desirable if such mechanism were able to reduce jerkiness while correctly identifying intended camera motion.